gluPartialDisk
renders a partial disk on the $ z ~=~ 0 $ plane. A partial disk is similar
to a full disk, except that only the subset of the disk from start through
start + sweep is included (where 0 degrees is along the +yaxis, 90 degrees
along the +x axis, 180 degrees along the -y axis, and 270 degrees along
the -x axis).

The partial disk has a radius of outer, and contains a concentric
circular hole with a radius of inner. If inner is 0, then no hole is generated.
The partial disk is subdivided around the z axis into slices (like pizza
slices), and also about the z axis into rings (as specified by slices
and loops, respectively).

With respect to orientation, the +z side of the
partial disk is considered to be outside (see gluQuadricOrientation). This
means that if the orientation is set to GLU_OUTSIDE, then any normals
generated point along the +z axis. Otherwise, they point along the -z axis.

If texturing is turned on (with gluQuadricTexture), texture coordinates
are generated linearly such that where $ r ~=~ "outer" $, the value at
(r, 0, 0) is (1.0, 0.5), at (0, r, 0) it is (0.5, 1.0), at (-r, 0, 0) it is
(0.0, 0.5), and at (0, -r, 0) it is (0.5, 0.0).